Cleaning apparatus and high pressure cleaner for use therein

ABSTRACT

A cleaning apparatus in which a cleaning process is simplified, a time required for the cleaning process is reduced and which has an excellent cleaning effect, and a high pressure cleaner for use therein are provided. The cleaning apparatus comprises a liquid carbon dioxide (CO 2 ) supply source and a gaseous CO 2  supply source, a high pressure pump changing CO 2  supplied from the liquid CO 2  supply source to CO 2  having high pressure, a cleaning additive supply source and a rinsing additive supply source, a homogeneous transparent phase mixer forming a supercritical homogeneous transparent phase mixture by mixing a cleaning additive supplied from the cleaning additive supply source and supercritical CO 2  supplied from the liquid CO 2  supply source, or forming a supercritical rinsing mixture by mixing a rinsing additive supplied from the rinsing additive supply source and supercritical CO 2  supplied from the liquid CO 2  supply source, a high pressure cleaner cleaning using the supercritical homogeneous transparent phase mixture supplied from the homogeneous transparent phase mixer and performing rinsing using the supercritical rinsing mixture supplied from the homogeneous transparent phase mixer, a separator separating gaseous CO 2  from a mixture discharged from the high pressure cleaner, and a CO 2  condenser condensing the separated CO 2 .

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2006-0006590, filed on Jan. 21, 2006, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cleaning apparatus and a highpressure cleaner for use therein, and more particularly, to a cleaningapparatus in which a cleaning process is simplified and a time requiredfor the cleaning process is reduced. The apparatus has an excellentcleaning effect and a high pressure cleaner for use therein.

2. Description of the Related Art

In a semiconductor wafer manufacturing process, a photoresist (PR) layershould be formed on a semiconductor substrate and removed after apredetermined process. The process of removing the photoresist (PR)layer is referred to as a cleaning process. The cleaning process can beperformed after a variety of operations of the semiconductor wafermanufacturing process, such as a front end of the line (FEOL) operation,a back end of the line (BEOL) operation or ion implantation. Thecleaning process is a process in which contaminants, such as aphotoresist or photoresist residues, are removed from a surface of asubstrate in a ultra-fine pattern. To this end, a wet cleaning processusing water and various solvents and a dry cleaning process usingsupercritical carbon dioxide (CO₂) have been developed.

In a conventional wet cleaning method including an RCA method, acleaning process can be properly performed for purposes. However, manyproblems exist in that the conventional wet cleaning method is notsuitable for manufacture of an ultra large scale integrated circuit(ULSI). For example, in a wet cleaning process, wettability of cleaningfluid to a fine structure having a high aspect ratio is lowered, and dueto repeated rinsing and drying processes, unwanted particles aregenerated. In addition, there are problems concerning metalinadvertently contaminated by a liquid-phase chemical solution, watermarks and corrosion, costs for ultra-pure purification and high puritypurification of chemicals. Process equipment clusterization is noteasily performed because of the large size of equipment and complicatedprocess. In addition, there are problems with environmentalcontamination caused by waste water and waste fluid and costs fortreating waste water.

In addition, since a large quantity of chemical solvent is used in aconventional RCA cleaning method, problems exist in that a wafer may bedamaged and a photoresist layer may not be completely removed. Toaddress the problems, new solvent has been developed. However, in theconventional wet cleaning process, due to a characteristic of themolecular structure of cleaning fluid, molecules of the cleaning fluidcannot easily infiltrate an ultra-fine structure less than 65 nm. Inparticular, it is not easy to clean copper for manufacturing a highperformance semiconductor in a next generation fine pattern having alow-K dielectric layer material.

To address the problems, the development of plasma, gaseous orsupercritical dry cleaning technology is needed. However, when aphotoresist is removed using an oxygen plasma ashing method used in adry cleaning process, a wafer is damaged and contaminated by oxygenplasma, and due to the existence of contaminants, an additional wetcleaning process needs to be performed. In addition, damages due to awet method or a plasma dry cleaning process do not occur in a cleaningprocess using the oxidation action of ozone that has been recentlydeveloped. However, problems such as environmental contamination causedby ozone exist.

During semiconductor manufacture, processes such as dry etching or wetetching, ashing or ion implantation are performed, and photoresist mayremain on a wafer. Accordingly, conventionally, a partial drying processand a wet process, that is, two processes such as ashing and organicstrip processes, are performed to remove the photoresist and thus, thenumber of processes is increased, resources are consumed and numerouscosts for waste water treatment are needed.

In addition, when wet cleaning is accompanied as described above, anadditional drying process, such as spin drying, isopropyl alcohol (IPA)vapor drying, or marangoni drying, is needed. In these drying methods,water marks are left and strain is generated and the possibility ofrecontamination caused by an electrostatic force is high. In particular,in the case of IPA vapor drying, a high temperature (greater than 200°C.) for IPA vaporization should be maintained and a large amount of IPAis required.

A semiconductor wafer cleaning method using a supercritical process inwhich supercritical CO₂ and several common solvent are mixed has beenalready introduced. However, because a homogeneous transparent phasecannot be formed by simply mixing polar common solvent withsupercritical nonpolar CO₂, problems concerning the conventional wetcleaning process are not solved and cleaning efficiency is low. Eventhough a homogeneous transparent phase supercritical state is formed, atemperature greater than 100° C. and a pressure greater than 300 bar areneeded and thus, costs are increased. To address these problems, evenwhen a surfactant is introduced, an additional mixer or a ultrasonicdevice is needed so as to form a supercritical homogeneous transparentphase and thus, manufacturing time is increased.

In addition, high purity (greater than 99.99%) CO₂ is used tomanufacture a semiconductor. In the prior art, an efficient purificationprocess of purifying and recovering used CO₂ to reuse CO₂ cannot beperformed.

SUMMARY OF THE INVENTION

The present invention provides a cleaning apparatus in which a cleaningprocess is simplified and a time required for the cleaning process isreduced. The apparatus has an excellent cleaning effect and a highpressure cleaner for use therein.

According to an aspect of the present invention, there is provided acleaning apparatus comprising: a liquid carbon dioxide (CO₂) supplysource and a gaseous CO₂ supply source; a high pressure pump changingCO₂ supplied from the liquid CO₂ supply source to CO₂ having highpressure; a cleaning additive supply source and a rinsing additivesupply source; a homogeneous transparent phase mixer forming asupercritical homogeneous transparent phase mixture by mixing a cleaningadditive supplied from the cleaning additive supply source andsupercritical CO₂ supplied from the liquid CO₂ supply source, or forminga supercritical rinsing mixture by mixing a rinsing additive suppliedfrom the rinsing additive supply source and supercritical CO₂ suppliedfrom the liquid CO₂ supply source; a high pressure cleaner cleaningusing the supercritical homogeneous transparent phase mixture suppliedfrom the homogeneous transparent phase mixer and performing rinsingusing the supercritical rinsing mixture supplied from the homogeneoustransparent phase mixer; a separator separating gaseous CO₂ from amixture discharged from the high pressure cleaner; and a CO₂ condensercondensing the separated CO₂.

The cleaning apparatus may further comprise at least one of a cleaningcolumn and an adsorption column for purifying CO₂ separated by theseparator.

CO₂ condensed in the CO₂ condenser may be provided to the liquid CO₂supply source and may be re-used.

The cleaning apparatus may further comprise a heater heating CO₂supplied from the liquid CO₂ supply source, the cleaning additivesupplied from the cleaning additive supply source, and the rinsingadditive supplied from the rinsing additive supply source.

The homogeneous transparent phase mixer may form the supercriticalhomogeneous transparent phase mixture by mixing the cleaning additivesupplied having atmospheric pressure or a low pressure less than 10 barwith the supercritical CO₂ having high pressure of 120 to 300 bar, usinga large pressure difference therebetween.

The cleaning apparatus may further comprise a pressure regulating valveconnected to the high pressure cleaner and regulating pressure insidethe high pressure cleaner.

The cleaning apparatus may further comprise: a circulation lineconnecting an outlet of the high pressure cleaner to a middle pointbetween the high pressure cleaner and the homogeneous transparent phasemixer; and a circulation pump connected to the circulation line.

An internal or external circulation unit may be provided to thehomogeneous transparent phase mixer.

According to another aspect of the present invention, there is provideda high pressure cleaner comprising: a wafer loading device on which awafer to be cleaned is loaded and which includes a protrusion; an upperelement including an inlet through which a mixture is injected in adownward direction, a wafer loading device fixing unit in which theprotrusion of the wafer loading device is inserted and which enables thewafer loading device to be fixed therein, and a pneumatic cylinderinsertion unit in which a pneumatic cylinder sliding from a side isinserted; an ascending and descending pneumatic cylinder moving theupper element in upward and downward directions; a lower elementincluding a pneumatic cylinder insertion unit in which a pneumaticcylinder sliding from a side is inserted and an outlet through which amixture is discharged and forming a space between the lower element andthe upper element in which the wafer loading device can be disposed; andan adherent type pneumatic cylinder sliding into the pneumatic cylinderinsertion unit of the upper element and the pneumatic cylinder insertionunit of the lower element and combining the upper element and the lowerelement when the upper element descends and is engaged with the lowerelement.

The high pressure cleaner may further comprise a sealant disposedbetween an edge of a surface of the upper element in a direction of thelower element and an edge of a surface of the lower element in adirection of the upper element and sealing a space between the upperelement and the lower element from the outside.

The high pressure cleaner may further comprise a first bended portiondisposed at an edge of a surface of the upper element in a direction ofthe lower element, and a second bended portion disposed at an edge of asurface of the lower element in a direction of the upper element, and afirst sealant and a second sealant disposed in the first bended portionand the second bended portion, respectively.

A groove may be formed in a circumferential direction of the waferloading device on a surface of the wafer loading device in a directionof the upper element, and a plurality of spray outlets may be providedalong the groove.

The inlet of the upper element may be provided so that a materialinjected through the inlet of the upper element is injected in adirection of the groove of the wafer loading device.

The upper element may further comprise an upper element guide pin andthe lower element may further comprise a guide pin insertion portion inwhich the upper element guide pin is inserted.

The inlet and the outlet may be provided in opposite directions.

The high pressure cleaner may further comprise a heating source and acooling source controlling temperature of the high pressure cleaner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic view of a cleaning apparatus used in a cleaningprocess according to an embodiment of the present invention;

FIG. 2 is a schematic view of a cleaning apparatus used in a cleaningprocess according to another embodiment of the present invention;

FIG. 3 is a front view of a high pressure cleaner included in thecleaning apparatus illustrated in FIG. 2;

FIG. 4A is a front view of an upper element of the high pressure cleanerillustrated in FIG. 3;

FIG. 4B is a bottom view of the upper element of the high pressurecleaner illustrated in FIG. 3;

FIG. 5A is a cross-sectional view of a lower element of the highpressure cleaner illustrated in FIG. 3;

FIG. 5B is a plan view of the lower element of the high pressure cleanerillustrated in FIG. 3;

FIG. 6A is a schematic view of a combined structure of the upper elementillustrated in FIG. 4A, the lower element illustrated in FIG. 5A and awafer loading device;

FIG. 6B is a plan view of a wafer loading device illustrated in FIG. 6A;

FIG. 7A is a front view of a modified example of FIG. 6A;

FIG. 7B is a plan view of the wafer loading device illustrated in FIG.7A;

FIG. 8 is a graph of time versus pressure with respect to all sectionsof a cleaning process using the cleaning apparatus illustrated in FIG.2;

FIG. 9 is a photo of a supercritical homogeneous transparent phasemixture used in a supercritical cleaning process;

FIG. 10A is a cross-sectional photo showing a wafer that has gonethrough a back-end-of-the-line (BEOL) process but is not cleaned using acleaning process according to an embodiment of the present invention;

FIGS. 10B through 10E are cross-sectional photos showing the case wherethe wafer of FIG. 10A has been cleaned using a cleaning processaccording to an embodiment of the present invention;

FIG. 10F is a cross-sectional photo showing the case where a wafer hasbeen cleaned using a conventional wet cleaning process;

FIG. 10G is a cross-sectional photo showing the case where the wafer ofFIG. 10A has been cleaned using a cleaning process that does not satisfyconditions according to an embodiment of the present invention;

FIG. 11A is a cross-sectional photo showing a wafer that has gonethrough a front-end-of-the-line (FEOL) process but is not cleaned usingthe cleaning process according to an embodiment of the presentinvention;

FIG. 11B is a photo of the surface of the wafer illustrated in FIG. 11A;

FIG. 11C is a cross-sectional photo showing the case where the wafer ofFIGS. 11A and 11B has been cleaned using the cleaning process accordingto an embodiment of the present invention;

FIG. 11D is a photo of the surface of the wafer illustrated in FIG. 11C;

FIG. 12A is a photo of the surface of a wafer that has gone through apost ion implantation process but is not cleaned using a cleaningprocess according to an embodiment of the present invention; and

FIGS. 12B and 12C are photos of the surface of the wafer of FIG. 12Athat has been cleaned using a cleaning process according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

FIG. 1 is a schematic view of a cleaning apparatus used in a cleaningprocess according to an embodiment of the present invention. Referringto FIG. 1, the cleaning apparatus includes a high pressure cleaner 60, agaseous carbon dioxide (CO₂) supply source 20 and a liquid CO₂ supplysource 21 which are connected to the high pressure cleaner 60, a highpressure pump 24 for supplying high pressure CO₂, a cleaning additivesupply source 25 for supplying an additive for cleaning and a rinsingadditive supply source 26 for supplying an additive for rinsing, heaters31, 32, and 33 installed on supply lines L2, L3, and L4, respectively,to heat CO₂ and additives, a homogeneous transparent phase mixer 70 forsupplying a predetermined amount of cleaning additive while forming asupercritical homogeneous transparent phase mixture, a pressureregulating valve 54 connected to the high pressure cleaner 60 tomaintain a predetermined pressure, a separator 61 connected to the highpressure cleaner 60 to separate gaseous CO₂ and a liquid-phase additivefrom a mixture discharged from the high pressure cleaner 60, a gasscrubbing column 63 and an adsorption column 64 for purifying theseparated gaseous CO₂, a CO₂ condenser 23 for condensing and reusing thepurified gas, a heating medium, a coolant supplier, and on-off automaticvalves 1 to 12.

A supercritical state is a state existing at a point greater than acritical temperature and a critical pressure. Properties of asupercritical fluid are very different from those of a fluid in a normalstate. That is, properties of the supercritical fluid, such as densityof a fluid, viscosity, solubility, thermal capacity or dielectricconstant, vary rapidly. The supercritical fluid state is a stateexisting at a point greater than the critical temperature and thecritical pressure. The critical temperature is temperature at which gasis not liquefied even though pressure is increased, and the criticalpressure is pressure at which liquid is not vaporized even thoughtemperature is raised. For example, the critical temperature of CO₂ isabout 31.06° C. and the critical pressure of CO₂ is about 73.8 bar. Thesupercritical fluid is a fluid in which a gaseous state and a liquidstate cannot be discriminated from each other. The supercritical fluidhas a similar characteristic to that of a liquid in that it has largesolubility. In addition, the supercritical fluid has similarcharacteristics to that of a gas in that it has low viscosity, largediffusivity, and low surface tension and can easily infiltrate a finestructure.

The gaseous CO₂ supply source 20 and the liquid CO₂ supply source 21 areconnected to the high pressure cleaner 60 via supply lines L1 and L2.The cleaning additive supply source 25 and the rinsing additive supplysource 26 are connected to the supply line L3 and supply a cleaningadditive and a rinsing additive to the homogeneous transparent phasemixer 70 via a cleaning additive supply pump 27 and a rinsing additivesupply pump 28. The homogeneous transparent phase mixer 70 connected tothe high pressure cleaner 60 forms a supercritical homogeneoustransparent phase mixture by mixing the cleaning additive havingatmospheric pressure or a low pressure state with the supercritical CO₂by using a large pressure difference therebetween. In addition, thehomogeneous transparent phase mixer 70 may form a supercritical rinsingmixture by mixing the rinsing additive and the supercritical CO₂, and aprocess thereof will be described later.

The cleaning apparatus of FIG. 1 may further include a circulation lineL8 and a circulation pump 29, as illustrated in FIG. 2 which is aschematic view of a cleaning apparatus used in a cleaning processaccording to another embodiment of the present invention. Thecirculation line L8 and the circulation pump 29 are connected to thehomogeneous transparent phase mixer 70. The circulation line L8 and thecirculation pump 29 enable the supplied supercritical homogeneoustransparent phase mixture to be stabilized by formation of an externalcirculation flow of the high pressure cleaner 60 and a mixing effect anda heat exchanging effect to be improved.

A cleaning process performed using the cleaning apparatus will now bedescribed in detail.

First, a wafer is loaded in the high pressure cleaner 60, which will bedescribed later below.

If the wafer is loaded in the high pressure cleaner 60, high-puritygaseous CO₂ (greater than 99.99%) having low pressure (less than 20psig) by the pressure regulators 52 and 53 is injected into the highpressure cleaner 60 via the corresponding on-off automatic valves 3 and4 and the supply line L1 from the gaseous CO₂ supply source 20. Thiscauses fine contaminants inside the high pressure cleaner 60 to beremoved. If the high pressure cleaner 60 is sealed (a process thereofwill be described later), high-purity gaseous CO₂ having high pressure(about 30-50 bar) is injected into the high pressure cleaner 60. Thiscauses a mixed fluid to smoothly flow into the high pressure cleaner 60,which will be described later.

The cleaning additive and the supercritical CO₂ having higher pressurethan a supercritical cleaning pressure (pressure in a cleaning processin the high pressure cleaner 60 is, preferably, about 120-300 bar) isinjected into the homogeneous transparent phase mixer 70, which will bedescribed later. The supercritical CO₂ is supplied from the CO₂condenser 23. That is, the supercritical CO₂ is automatically suppliedfrom the CO₂, condenser 23 by opening and closing the on-off automaticvalves 1, 2, 5, and 8 installed on the supply line L2 and via the highpressure pump 24 for supplying CO₂. The supercritical CO₂ may be heatedby the heater 31 to become the supercritical CO₂, before it reaches thehomogeneous transparent phase mixer 70.

The gaseous CO₂ supplied from the gas scrubbing column 63 and theadsorption column 64 is condensed using a refrigerant in the CO₂condenser 23 and thus, the supercritical CO₂ is formed. At this time,initial liquid CO₂ and CO₂ corresponding to wasted CO₂ in a cleaningprocess are supplied from the liquid CO₂ supply source 21 via the liquidCO₂ supplementing valve 51.

The supercritical CO₂ is mixed with the cleaning additive and becomes asupercritical homogeneous transparent phase mixture for use in acleaning process in the sealed high pressure cleaner 60. In addition,the supercritical CO₂ is mixed with the rinsing additive and becomes asupercritical rinsing mixture for use in the cleaning process in thesealed high pressure cleaner 60.

The additives are automatically supplied from the cleaning additivesupply source 25 and the rinsing additive supply source 26 via theon-off automatic valves 6 and 7 installed on the supply lines L3 and L4and the quantity regulating supply lines. In this case, the supplied CO₂and the additives are heated by the heaters 31, 32, and 33 installed onthe supply lines L2, L3, and L4, respectively, or by a line heater at apredetermined temperature or temperature in a predetermined range (forexample, about 35-100° C.).

The cleaning additive is instantaneously mixed by the homogeneoustransparent phase mixer 70 with the supercritical CO₂ at a largepressure difference and becomes a supercritical homogeneous transparentphase mixture flowing into the high pressure cleaner 60 and used in thecleaning process. More specifically, the cleaning additive havingatmospheric pressure or a low pressure less than 10 bar is supplied tothe homogeneous transparent phase mixer 70 and then, the CO₂ having ahigher pressure than the supercritical cleaning pressure is supplied tothe homogeneous transparent phase mixer 70 so that the supercriticalhomogeneous transparent phase mixture can be formed using a mixingeffect caused by a large pressure difference.

In general, since the supercritical CO₂ is nonpolar and the cleaningadditive is polar, a higher super-high temperature and pressure thanthat used in the above-described conditions are needed to mix thesupercritical CO₂ and the cleaning additive. As such, cleaning costs aregreatly increased. Accordingly, to address these problems, in thecleaning process according to the present embodiment, the cleaningadditive further includes a surfactant so that the supercriticalhomogeneous transparent phase mixture can be easily formed under theabove-described cleaning conditions such as super-high pressure andsuper-high temperature. In addition, the cleaning additive and thesupercritical CO₂ are mixed with each other using a large pressuredifference in the homogeneous transparent phase mixer 70 so that thesupercritical homogeneous transparent phase mixture can be easily formedwithin a short time without using an additional mixer or an ultrasonicdevice.

To this end, the cleaning additive may include a fluoride groupsurfactant. The fluoride group surfactant may use fluoride groupcarboxylic acid having a carbon number 2 to 20, perfluoro ether polymerhaving an average molecular weight of 300 to 5000 or a mixture thereof.

The composition of the cleaning additive will now be described ingreater detail. The cleaning additive may include fluorosurfactant 0.01to 90 wt %, aliphatic amine 0.01 to 15 wt %, polar organic solvent 0.01to 15 wt %, alcohol-based solvent 0.1 to 20 wt %, ether-based solvent0.1 to 30 wt %, anticorrosive agent 0 to 5 wt %, and water 0 to 15 wt %.In the present embodiment, the fluorosurfactant is fluoride groupcarboxylic acid having a carbon number of 2 to 20, perfluoro ethersystem polymer having an average molecular weight of 300 to 5000 or amixture thereof. The aliphatic amine is monoethanolamine,2-(2-aminoethoxy) ethanol, diethanolamine, amino bis propylamine,2-methylaminoethanol, triethylaminoethanol or a mixture thereof. Thepolar organic solvent is N,N′-dimethylacetamide, dimethylsulfuroxide,1-methyl-2-pyrrolidinone, N,N′-dimethylformamide, ammonium fluoride or amixture thereof. The alcohol-based solvent is methanol, ethanol,isopropanol or a mixture thereof. The ether-based solvent isethyleneglycol methylether, ethyleneglycol ethylether, ethyleneglycolbutylether, diethyleneglycol methylether, diethylenglycol ethylether,triethyleneglycol methylether, triethyleneglycol ethylether or a mixturethereof. The anticorrosive agent is catechol, gallic acid or a mixturethereof.

Of course, a cleaning additive having a different composition from thecomposition described above may be used. For example, the cleaningadditive may include fluorosurfactant 0 to 90 wt %, semiconductorcleaning stripper 0.1 to 15 wt %, alcohol-based solvent 0.1 to 20 wt %,and water 0 to 15 wt %. In this case, the fluorosurfactant is fluoridegroup carboxylic acid having a carbon number of 2 to 20, perfluoro ethersystem polymer having an average molecular weight of 300 to 5000 or amixture thereof. The alcohol-based solvent is methanol, ethanol,isopropanol or a mixture thereof.

The volume of the cleaning additive in the supercritical homogeneoustransparent phase mixture in which the cleaning additive and thesupercritical CO₂ are mixed may be 2 to 30 percent by volume.

The homogeneous transparent phase mixer 70 for forming the supercriticalhomogeneous transparent phase mixture by mixing the cleaning additiveand the supercritical CO₂ is a high pressure vessel like a high pressurecylinder, and so on. In this case, a heating source may be attached tothe homogeneous transparent phase mixer 70 and the homogeneoustransparent phase mixer 70 may be adjusted to a predeterminedtemperature or to a temperature in a predetermined range. A minimumspace is provided in which the fixed quantity of the cleaning additiveneeded for cleaning can be supplied, the cleaning additive can be mixedwith the supercritical CO₂ and the supercritical homogeneous transparentphase mixture can be formed. In addition, if necessary, an internal orexternal circulation unit may be further provided in the homogeneoustransparent phase mixer 70 so as to maximize a mixing effect and a heatexchanging effect.

If the supercritical homogeneous transparent phase mixture is directlyinjected into the high pressure cleaner 60, due to a large pressuredifference, the supercritical homogeneous transparent phase mixture isnot maintained and is deformed. In order to prevent this problem, beforethe supercritical homogeneous transparent phase mixture is injected intothe high pressure cleaner 60, CO₂ having a lower pressure than asupercritical cleaning pressure is injected into the high pressurecleaner 60 via an auxiliary line L6 using 3-way on-off automatic valves5 and 8 on the supply line L2. At this time, the pressure in the highpressure cleaner 60 is regulated to a predetermined pressure or to apressure in a predetermined range (for example, pressure less than 10 to40 bar of the supercritical cleaning pressure) using the pressureregulating valve 54.

Before the supercritical homogeneous transparent phase mixture isinjected into the high pressure cleaner 60, CO₂ having a lower pressurethan the supercritical cleaning pressure is injected into the highpressure cleaner 60 such that the supercritical homogeneous transparentphase mixture is not deformed and is maintained and cleaning can beeffectively performed. In this case, CO₂ is injected into the highpressure cleaner 60 at pressure lower than the supercritical cleaningpressure so that due to a pressure difference, the supercriticalhomogeneous transparent phase mixture can be naturally injected into thehigh pressure cleaner 60.

The supercritical homogeneous transparent phase mixture as describedabove is injected into the high pressure cleaner 60 in which thesupercritical CO₂ is charged and can be used in a non-circulating statein a cleaning process without an additional device. Unlike FIG. 1, anexternal circulation flow is formed using the circulation line L8 andthe circulation pump 29 and a cleaning operation is performed so thatthe homogeneous transparent phase mixture supplied to the high pressurecleaner 60 can be stably maintained and a mixing effect and a heatexchanging effect can be improved.

If a photoresist or etch residues on the wafer are removed using thecleaning operation, the cleaning additive and cleaning contaminants suchas a solvated photoresist residues need not to remain in the surface ofthe wafer. To this end, the homogeneous transparent phase mixer 60 mixesthe rinsing additive supplied from the rinsing additive supply source 26and the supercritical CO₂ so that a supercritical rinsing mixture can beformed and injected into the high pressure cleaner 60 and a cleaningmixture is removed. The supercritical rinsing mixture containing thesupercritical CO₂ and the mainly alcohol-based rinsing additive can beformed by simple mixture of the rinsing additive and the supercriticalCO₂. The rinsing process may be performed using the supercriticalrinsing mixture having pressure of about 80 to 250 bar.

Then, the cleaning additive mixture that may exist on the surface of thewafer can be removed using only the supercritical CO₂.

Gaseous CO₂ and a liquid-phase additive are separated by the separator61 from the mixture discharged from the high pressure cleaner 60 afterthe cleaning and rinsing operations. At this time, pressure inside thehigh pressure cleaner 60 is reduced at a temperature of about 35° C. sothat CO₂ is removed from the high pressure cleaner 60 in a gaseous statewithout phase transition to a liquid state. Unlike a conventionalcleaning process, an additional drying device or operation is notrequired and problems such as formation of water marks that may occurafter wet etching can be mostly prevented.

The separator 61 is used to separate a mixture in a high pressure state.A high pressure cleaning mixture (finally becoming high pressure CO₂)used in cleaning, rinsing, and dry operations is discharged into theseparator 61 from the high pressure cleaner 60 using an automaticoperation of the 3-way on-off automatic valve 11 and is purified andre-used. High-pressure gaseous CO₂ is finally discharged by changing adirection of the 3-way on-off automatic valve 11 and is separatelytreated.

The high pressure CO₂ separated from the separator 61 in an upwarddirection is transferred into the gas scrubbing column 63 via a backpressure regulator 55 attached to a connection line of an upperdischarging portion of the separator 61 and the back pressure regulator55 adjusting pressure. The liquid-phase additive separated from a lowerportion of the separator 60 using an automatic operation of the on-offautomatic valve 12 is purified and re-used via an additional treatmentprocess or is discharged during general post-processing performed in anexisting semiconductor manufacturing factory. In this case, a heatingsource is attached to the discharge line L7 and the separator 61 andlatent heat loss caused by insulation expansion of the supercritical CO₂or the liquid CO₂ is compensated for and discharge in a gaseous state issmoothly induced.

The gaseous CO₂ separated from the separator 61 goes through a purifyingprocess. That is, the gaseous CO₂ moves toward the gas scrubbing column63 via the back pressure regulator 55 and impurities of the gaseous CO₂are primarily removed. The gaseous CO₂ moves toward the adsorptioncolumn 64 and impurities of the gaseous CO₂ are secondarily removed andit becomes high purity gaseous CO₂ (greater than 99.99%). Of course,only one of the gas scrubbing column 63 and the adsorption column 64 canbe used. That is, purification can be performed simply using theadsorption column 64. Whether or not purification is performed simplyusing only the adsorption column 64 is determined depending on thecomponents of an additive that can be changed according to the wafer tobe cleaned or formation of a volatile gas caused by a cleaning reaction.

After the cleaning process is performed, the high purity gaseous CO₂ iscondensed by the CO₂ condenser 23 into a liquid state using acirculation coolant system and re-circulated for another cleaningprocess.

According to the cleaning process according to an embodiment of thepresent invention, a conventional two-step process including a plasmaashing process (a drying process) and a wet process used in removing aphotoresist or residues can be substituted for a one-step drying processusing a supercritical homogeneous transparent phase mixture. Inaddition, the cleaning, rinsing, and drying processes are continuouslyperformed in a single high pressure cleaner. Thus, an additional dryingapparatus and process are not required. CO₂ that goes throughpressurization and depression processes does not leave any residuebecause of phase change.

When only the supercritical CO₂ is used in the cleaning process, acleaning effect is restricted. However, in the cleaning processaccording to the present embodiment, the cleaning process is performedby mixing the supercritical CO₂ and the cleaning additive so that thecleaning effect can be maximized. In this case, the supercritical CO₂ isnonpolar and the cleaning additive is generally polar. Thus, a highersuper-high pressure and super-high temperature than those of theabove-described conditions are required so that the supercritical CO₂and the cleaning additive can be mixed and a supercritical state can bemaintained. As such, cleaning costs are greatly increased. To addressthese problems, in the cleaning process according to the presentembodiment, the cleaning additive includes the surfactant so that thesupercritical homogeneous transparent phase mixture can be easily formedand maintained even under the above-described cleaning conditions. Inthis case, the cleaning additive and the supercritical CO₂ are mixed inthe homogeneous transparent phase mixer 70 using a large pressuredifference such that the supercritical homogeneous transparent phasemixture can be easily formed within a short time without using anadditional mixer or an ultrasonic device.

The cleaning process according to the present embodiment is used so thatthe homogeneous transparent phase of the supercritical homogeneoustransparent phase mixture can be easily formed and maintained within ashort time and an automatic cleaning apparatus and an automatic valveare designed and configured and the cleaning process can be easilyperformed using process automation together with a control system.

In addition, a high diffusivity of the supercritical CO₂ is used so thatthe limit that semiconductor chemicals can infiltrate a fine structureis overcome, wettability of the fine structure is maximized using lowsurface tension and super fine cleaning required in forming andmanufacturing patterns of a super fine structure can be performedaccordingly.

In order to remove photoresist and residues using only puresupercritical CO₂ or the supercritical fluid mixture in which ahomogeneous transparent phase is not easily formed, a combination of thecleaning additive including the surfactant presented in Table 1, whichwill be described later, can be used.

The structure of the high pressure cleaner 60 and cleaning inside thehigh pressure cleaner 60 will now be described.

FIG. 3 is a front view of the high pressure cleaner 60 illustrated inFIGS. 1 and 2, FIG. 4A is a front view of an upper element of the highpressure cleaner 60 illustrated in FIG. 3, FIG. 4B is a bottom view ofthe upper element of the high pressure cleaner 60 illustrated in FIG. 3,FIG. 5A is a cross-sectional view of a lower element of the highpressure cleaner 60 illustrated in FIG. 3, and FIG. 5B is a plan view ofthe lower element of the high pressure cleaner 60 illustrated in FIG. 3.FIG. 6A is a schematic view of a combined structure of the upper elementillustrated in FIG. 4A, wherein the lower element illustrated in FIG. 5Aand a wafer loading device, FIG. 6B is a plan view of the wafer loadingdevice illustrated in FIG. 6A, FIG. 7A is a view of a modified exampleof FIG. 6A, and FIG. 7B is a schematic plan view of the wafer loadingdevice illustrated in FIG. 7A.

The high pressure cleaner 60 includes an upper element 101 and a lowerelement 102. The upper element 101 makes a vertical motion using anupper element-ascending and descending pneumatic cylinder 105. If theupper element 101 descends, an adherent type pneumatic cylinder 106 isslid into an adherent type pneumatic cylinder insertion portion 107 foreach of the upper element 101 and the lower element 102 so that theupper element 101 and the lower element 102 are combined with each otherand fixed. If necessary, an upper element guide pin 230 is provided inthe upper element 101 of the high pressure cleaner 60 and a guide pininsertion portion 231 is provided in the lower element 102 so that theupper element guide pin 230 can be inserted into the guide pin insertionportion 231 and the upper element 101 and the lower element 102 can becombined with each other in a correct position. In addition, a heatingsource or a cooling source 108 is attached to the high pressure cleaner60 so that the high pressure cleaner 60 can be adjusted at apredetermined temperature or at a temperature in a predetermined range.In this case, as illustrated in FIG. 3, the heating source or thecooling source 108 may have a shape which surrounds the lower element102 of the high pressure cleaner 60 and into which a heating medium orcoolant flows the heating source or the cooling source 108. Coils havinga large resistance may be used as the heating source and a variety ofmodifications is possible.

The inner or outer diameter of the high pressure cleaner 60 may bedifferent according to the diameter of a wafer to be cleaned. The numberof adherent type pneumatic cylinders 106 which combine the upper element101 and the lower element 102 with each other may be different accordingto the size of the wafer to be cleaned. For example, about 6 to 8adherent type pneumatic cylinders 106 may be provided for an 8-inchwafer (see cylinder insertion portions 107 in FIGS. 4B and 5B).

As described above, a wafer is loaded in the high pressure cleaner 60before cleaning, that is, before the upper element 101 and the lowerelement 102 are combined with each other. The wafer to be cleaned isloaded in a wafer loading device 201 illustrated in FIGS. 6A and 6B. Thewafer loading device 201 is fixed when a pin (a protrusion 210) of thewafer loading device 201 is inserted into a wafer loading device fixingportion 210 a (see FIG. 4A). In this case, a screw thread is provided inthe pin 210 of the wafer loading device 201 and a screw groove isprovided in the wafer loading device fixing portion 210 a of the upperelement 101 so that the wafer loading device 201 can be more securelyfixed in the upper element 101. For your reference, a plurality of waferloading device fixing portions 210 a are shown in FIG. 4B. However, forexplanatory convenience, only two wafer loading device fixing portions210 a are shown in FIG. 4A.

If necessary, an auxiliary pin 211 is provided in the lower element 102,as illustrated in FIG. 5B, so that a wafer to be inserted into the waferloading device 201 can be supported by the auxiliary pin 211. Of course,only two auxiliary pins 211, as illustrated in FIG. 5B, need not to beprovided and a variety of modifications is possible.

The wafer loading device 201 may be a wafer loading device 201 on whicha sheet of wafer is loaded, as illustrated in FIG. 6A or a wafer loadingdevice 201 on which a plurality of wafers are simultaneously loaded, asillustrated in FIG. 7A.

After the wafer is loaded in the wafer loading device 201, high purity(greater than 99.99%) gaseous CO₂ having low pressure (less than 20psig) using pressure regulators 52 and 53 (see FIGS. 1 or 2) primarilyflows into the high pressure cleaner 60 from the gaseous CO₂ supplysource 20 (see FIGS. 1 or 2) when the upper element 101 descends. Assuch, fine contaminants inside the high pressure cleaner 60 are removed.When the upper element 101 and the lower element 102 of the highpressure cleaner 60 are engaged with each other, the upper element 101and the lower element 102 are combined with each other using theadherent type pneumatic cylinder 106.

Then, the high purity gaseous CO₂ having high pressure (about 30 to 50bar) flows into the high pressure cleaner 60, and CO₂ having lowpressure (for example, pressure lower than supercritical cleaningpressure of 120 to 300 bar by 10 to 40 bar) flows into the high pressurecleaner 60 so that the supercritical homogeneous transparent phasemixture to flow is not deformed. In this case, pressure of the highpressure cleaner 60 is regulated at a predetermined pressure or at apressure in a predetermined range using the pressure regulating valve54. Then, the supercritical homogeneous transparent phase mixture flowsinto the high pressure cleaner 60 so that cleaning can be performed.

At this time, the high pressure cleaner 60 should be completely sealedso that the CO₂ Of the supercritical homogeneous transparent phasemixture flowing into the high pressure cleaner 60 cannot leak. To thisend, the high pressure cleaner 60 may further include a sealant. InFIGS. 6A and 7A, a first sealant 220 and a second sealant 221 areprovided. That is, a first bended portion is provided at an edge of asurface of the upper element 101 in a direction of the lower element102, and a second bended portion is provided at an edge of a surface ofthe lower element 102 in a direction of the upper element 101. The firstsealant 220 and the second sealant 221 are provided in the first bendedportion and the second bended portion, respectively. The first sealant220 and the second sealant 221 may have a variety of shapes. In FIGS. 6Aand 7A, the first sealant 220 and the second sealant 221 have a “E:”shape.

A pressure-resistant energized Teflon seal or a metal seal may be usedfor the first sealant 220 and the second sealant 221. The energizedTeflon seal is formed of pure Teflon or Teflon in which a chargingmaterial is mixed. To ensure elasticity required as a restoring force ofthe first sealant 220 and the second sealant 221, the first sealant 220and the second sealant 221 may include a cantilever spring or helicoilspring having the same material as that of metal seal. When metal sealis used for the first sealant 220 and the second sealant 221, the firstsealant 220 and the second sealant 221 may be formed SUS316-basedstainless steel in which corrosion does not occur, Hastelloy-C orElgiloy depending on the composition of an additive.

Of course, a material for the first sealant 220 and the second sealant221 is not limited to this and a variety of materials of whichanticorrosive property and durability are excellent at a supercriticalhigh pressure and which can be sealed may be used for the first sealant220 and the second sealant 221.

As described above, high purity (greater than 99.99%) gaseous CO₂ havinglow pressure (less than 20 psig), high purity gaseous CO₂ of a highpressure (about 30 to 50 bar), CO₂ having low pressure than asupercritical cleaning pressure (for example, pressure lower than thesupercritical cleaning pressure of 120 to 300 bar by 10 to 40 bar), anda supercritical homogeneous transparent phase mixture flow into the highpressure cleaner via an inlet 110 provided in the upper element 101 ofthe high pressure cleaner 60.

The inlet 110 is connected to an upper portion of the wafer loadingdevice 201. A groove 202 a is formed in a circumferential direction ofthe wafer loading device 201, as illustrated in FIG. 6B, and a pluralityof spray outlets 202 are provided inside the groove 202 a in a directionof the top surface of a wafer to be loaded. The inlet 110 is provided sothat a material injected through the inlet 110 is injected in adirection of the groove 202 a of the wafer loading device 201. Thus, thematerial passing through the inlet 110 moves along the groove 202 a inthe circumferential direction of the wafer loading device 201 and thewafer that passes through the spray outlets 202 is cleaned. That is, thewafer cleaning device 201 divides the supercritical homogeneoustransparent phase mixture in the high pressure cleaner 60 and maximizesthe cleaning effect. Referring to FIGS. 7A and 7B which illustrates thecase where a plurality of wafers are loaded in one wafer loading device201, the spray outlets 202 are provided in a direction of each wafer tobe loaded so that, when the wafers are loaded in the wafer loadingdevice 201, each wafer can be effectively cleaned.

The supercritical homogeneous transparent phase mixture flows into thehigh pressure cleaner 60 and the homogeneous transparent phase ismaintained at a predetermined pressure or temperature, whereby eachwafer is cleaned. The supercritical homogeneous transparent phasemixture infiltrates photoresist polymer and expands so that thephotoresist polymer is decomposed or dissolved together with thecleaning additive. In this procedure, a photoresist on each wafer oretch residues are substantially removed.

If the photoresist or etch residues on each wafer are removed in thismanner, the cleaning mixture is removed using a supercritical rinsingmixture containing the rinsing additive supplied from the cleaningadditive supply source 26 and the supercritical CO₂. A rinsing additivemixture that may exist on the surface of the wafer is removed using onlythe supercritical CO₂.

The material used in the cleaning and rinsing processes is discharged tothe outside via an outlet 111 illustrated in FIGS. 5A and 5B andpost-processed as described above and re-used or separately processed.The position and shape of the outlet 111 are not limited to thoseillustrated in FIGS. 5A and 5B and a variety of modifications ispossible. In this case, as illustrated in FIG. 5B, the outlet 111 may bepositioned opposite to the position of the outlet 110 illustrated inFIG. 4B. To this end, the supercritical homogeneous transparent mixtureor the supercritical rinsing mixture injected through the inlet 110passes through the inside of the high pressure cleaner 60 and isdischarged to the outside so that cleaning and rinsing of the wafer canbe effectively performed.

By using the above-described high pressure cleaner 60 and the cleaningprocess and apparatus described above, the supercritical CO₂ and theadditive form the supercritical homogeneous transparent phase mixture sothat the surface of the wafer injected into the high pressure cleaner 60can be cleaned. In addition, unlike the prior art, the wet process isnot performed so that an excellent cleaning result can be obtained.

In addition, if the supercritical homogeneous transparent phase mixtureis formed in the homogeneous transparent phase mixer 70, the mixture issupplied as rapid flow onto the wafer via the spray type wafer loadingdevice 201 such that an excellent cleaning effect can be achieved evenin a non-circulating state (see FIG. 1). In addition, cleaning bycontact of the circulation flow (see FIG. 2) provides fluidity of themixture so that a contact effect of the mixture and the wafer ismaximized, the dissolved photoresist and photoresist residues arecontinuously removed and the cleaning effect is further enhanced.

As described above, the cleaning additive and contaminants that remainon the wafer after the cleaning process can be removed by supplying thesupercritical rinsing mixture which is a mixture of the supercriticalCO₂ and the cleaning additive. The rinsing additive that remains afterthe removing process can be removed by supplying only the supercriticalCO₂. The supercritical rinsing mixture used in this procedure isconducive to rinsing and auxiliary cleaning so that the cleaning effectis maximized.

Even in the rinsing process, the supercritical homogeneous transparentphase mixture is supplied by a spray type rapid flow like in thecleaning process so that a wafer to be cleaned can be cleaned by contactwith only a pump flow (see FIG. 1) or by contact with the pump flow andthe circulation flow (see FIG. 2).

The total process time including the cleaning time and the rinsing timemay be within 10 minutes.

FIG. 8 is a graph of time versus pressure with respect to all sectionsof a cleaning process, as described above, using the cleaning apparatusillustrated in FIG. 2. In FIG. 8, P_(c) is a supercritical pressure andP₀ is a desired supercritical cleaning pressure. P₁ is greater thanP_(c) and less than about 10 to 40 bar of cleaning pressure P₀, that is,P₂. P₁ is pressure in which the supercritical homogeneous transparentphase mixture formed in the homogeneous transparent phase mixer can bemaintained in a homogeneous transparent phase.

As described above, the cleaning process is performed in the state whereonly the supercritical CO₂ is primarily filled in the high pressurecleaner 60 up to pressure P₁ and the supercritical homogeneoustransparent phase mixture is filled in the high pressure cleaner 60 ashort time later. The rinsing process can be performed even under alower pressure than cleaning pressure P₀, as shown by the rinsingsection of FIG. 8. Of course, the process illustrated in FIG. 8 is anexample and the present invention is not limited to this.

Embodiments 1 to 4

An experiment for dry cleaning a wafer that had gone through aback-end-of-the-line (BEOL) process using a supercritical homogeneoustransparent phase mixture and removing photoresist residues having arabbit ears shape that remained after aluminium metal etching wascarried out.

The wafer had a layer structure of Si/Si rich oxide 4000 Å/Ti 300 Å/TiN900 Å/Al 8000 Å/Ti 100 Å/TiN 400 Å, and photoresist residues generatedin a metal etching process remained on the wafer.

In this case, a cleaning additive mixed with the supercritical CO₂ was aformulation of a surfactant, a stripper for semiconductor cleaning orco-solvent mixture, and ethanol. Only ethanol was used as a primaryrinsing additive mixed with the supercritical CO₂ and only thesupercritical CO₂ was used without any additive in a secondary rinsingprocess which is a final process.

The wafer under the above-described conditions was used, and a cleaningexperiment was carried out whereby different surfactant or rinsingconditions were used. The conditions were shown in Table 1 below.

TABLE 1 Classification Embodiment 1 Embodiment 2 Embodiment 3 Embodiment4 Composition of PFOA 83.5 monohydrated-PFOA PFHA 83.5 PFOA 82.7Cleaning additive Stripper 6.0 87.4 Stripper 6.0 MEA 2.5 (wt %) Ethanol10.5 Stripper 5.2 Ethanol 10.5 1-M-2-P 1.7 Ethanol 7.4 Ethanol 13.1Volume of cleaning 13.6% 16.2% 13.6% 13.6% additive Primary EthanolEthanol Ethanol Ethanol Rinsing additive Volume of primary 16.7% 16.7%16.7% 16.7% rinsing additive Cleaning conditions 55° C., 148 bar 51° C.,165 bar 54° C., 163 bar 52° C., 160 bar 3 min 3 min 3 min 3 min(non-circulating) (non-circulating) (non-circulating) (non-circulating)Primary rinsing 36° C. 45 ± 1° C. 42° C. 40 ± 1° C. conditions 132 ± 6bar 153 ± 12 bar 125 ± 3 bar 145 ± 5 bar 2 min(flow) 2 min(flow) 2min(flow) 2 min(flow) Secondary rinsing 39° C. 42° C. 46° C. 40 ± 3° C.,136 ± 6 bar conditions 122 ± 7 bar 148 ± 7 bar 121 ± 3 bar 2 min 2min(flow) 2 min(flow) 2 min(flow) (non-circulating)

Here, the primary rinsing process is a rinsing process using asupercritical homogeneous transparent phase mixture in which thecleaning additive and the supercritical CO₂ are mixed, and the secondaryrinsing process is a rinsing process using only the supercritical CO₂.PFOA is perfluorooctanoic acid, PFHA is perfluoroheptanoic acid, MEA ismonoethanolamine, and 1-M-2-P is 1-methyl-2-pyrrolidinone.

The premise of supercritical fluid cleaning and rinsing is to make andmaintain a homogeneous transparent phase mixture in which ingredients ofa supercritical fluid mixture are not separated. A photo of thesupercritical homogeneous transparent phase mixture formed in thecleaning process is shown in FIG. 9.

After the rinsing process, the result of observing the state before andafter the cleaning process using a scanning electron microscope (SEM) isshown in FIG. 10A (before cleaning), FIG. 10B (Embodiment 1), FIG. 10C(Embodiment 2), FIG. 10D (Embodiment 3), and FIG. 10E (Embodiment 4).Here, FIGS. 10B, 10C, and 10D show the result in which the cleaningprocess was carried out in the state where a cleaning additive wasformulated by using a stripper for semiconductor cleaning and ethanol asa co-solvent and by changing a surfactant, and FIGS. 10B, 10C, and 10Dshow different results according to a cleaning characteristic based onthe composition of the surfactant and the cleaning additive. FIG. 10Eshows the case where a stripper for semiconductor cleaning is not usedas a co-solvent but is selected and formulated by itself, as illustratedin the above Table 1.

Referring to FIG. 10A, which shows a wafer before the cleaning process,photoresist residues formed of polymer generated in the etching processremain on the surface of the wafer. The photoresist residues are shownin the form of rabbit ears-shaped contamination on the wafer.

FIGS. 10B through 10E are photos showing the case where a wafer has beencleaned using the supercritical homogeneous transparent phase mixtureunder the conditions of Table 1. As illustrated in FIGS. 10A through10E, an excellent cleaning effect in which all rabbit ears-shapedphotoresist residues are removed within 10 minutes of total processtime, is obtained.

Comparative Examples 1 and 2

FIG. 10F is a cross-sectional photo showing the case where a wafer hasbeen cleaned using a conventional wet cleaning process, and FIG. 10G isa cross-sectional photo showing the case after the wafer of FIG. 10A iscleaned using a cleaning process that does not satisfy conditionsaccording to an embodiment of the present invention.

FIG. 10F shows the case where the conventional wet cleaning process isperformed for 120 minutes using the cleaning additive used inEmbodiment 1. Even though the wet cleaning is performed for 120 minutes,unlike the cleaning result of Embodiments 1 and 2, photoresist residueshaving a rabbit ears shape remain. As such, a supercritical dry cleaningprocess according to the present invention shows an epoch-makingcleaning result compared to the conventional wet cleaning process.

FIG. 10G shows the case where a homogeneous transparent phase is notformed using a surfactant or by changing process conditions under theconditions of Embodiments 1 to 4, and cleaning is not satisfactory. Evenwhen a rinsing process according to the present embodiment is notperformed, a similar result to FIG. 10G is obtained. As such, it isessential for a dry cleaning process according to the present embodimentto form a homogeneous transparent phase.

Embodiment 5

An experiment for removing a photoresist on a wafer during a wafermanufacturing process that had gone through a front-end-of-the-line(FEOL) process using a supercritical homogeneous transparent phasemixture was carried out.

The wafer had a layer structure of Si/HLD 1000 Å/Nitride 4500 Å/BPSG21000 Å/PR 10500 Å. The wafer, which was a p-type wafer on which apositive photoresist was coated, was heat-treated at 120° C.

Just ethanol was used for the cleaning additive mixed in thesupercritical CO₂ according to an embodiment of the present invention,and a rinsing process was performed once only using supercritical CO₂.

Cleaning conditions are Table 2 below.

TABLE 2 Cleaning additive Ethanol Volume of cleaning additive (%) 13.6%Cleaning conditions 58° C., 150 bar, 2 min(non-circulating) Rinsingconditions 48 ± 1° C., 142 ± 6 bar, 2 min (flow)

FIG. 11A is a cross-sectional photo of a wafer that has gone through anFEOL process but is not cleaned using the cleaning process according toan embodiment of the present invention, and FIG. 11B is a photo of thesurface of the wafer illustrated in FIG. 11A. Referring to FIG. 11A, aphotoresist layer is formed on the wafer, and a groove is formed in thephotoresist layer. When viewing FIG. 11A, protrusions formed of aphotoresist having a circular cross-section are formed on the wafer asillustrated in FIG. 11B.

FIG. 11C is a cross-sectional photo of the case where the wafer of FIGS.11A and 11B has been cleaned using the cleaning process according to anembodiment of the present invention, and FIG. 11D is a photo of thesurface of the wafer illustrated in FIG. 11C. Referring to FIG. 11C, aphotoresist layer is completely removed, unlike FIG. 11A, and this canbe seen in FIG. 11D.

Embodiments 6 and 7

An experiment for cleaning a wafer that has gone through a post ionimplantation process using a supercritical homogeneous transparent phasemixture and for removing a photoresist or photoresist residues thatremain on an ion-implanted wafer during an arsenic (As) ion implantationprocess was carried out. The wafer has a variety of patterns including,in this case, numbers.

The wafer had a layer structure of Si/Oxide 5000 Å/Poly 2000 Å/PR 50000Å. An As ion implantation energy was 60 KeV, and the wafer doped withions of 5E13/cm that has gone through a post ion implantation processwas used.

The cleaning additive mixed with the supercritical CO₂ was formulationof a surfactant, a stripper for semiconductor cleaning or co-solventmixture, and ethanol. Only ethanol was used as a primary rinsingadditive mixed with the supercritical CO₂ and only the supercritical CO₂was used without any additive in a secondary rinsing process which is afinal process.

The cleaning process was performed so that a supercritical homogeneoustransparent phase mixture (FIG. 9) was formed and maintained, like inthe cleaning process (Embodiments 1 to 4) of the wafer that went througha BEOL process. The conditions were shown in Table 3 below.

TABLE 3 Classification Embodiment 6 Embodiment 7 Composition of cleaningadditive PFOA 83.5 PFOA 83.8 (wt %) Stripper 6.0 Stripper 7.1 Ethanol10.5 Ethanol 9.1 Volume of cleaning additive (%) 13.6% 17.5% Primaryrinsing additive Ethanol Ethanol Volume of primary rinsing additive (%)16.7% 16.7% Cleaning conditions 59° C. 50° C. 148 bar 150 bar 3 min(non-circulating) 3 min (non-circulating) Primary rinsing conditions 43± 3° C. 42° C. 125 ± 5 bar 150 ± 3 bar 2 min (flow) 2 min (flow)Secondary rinsing conditions 48 ± 3° C. 40° C. 122 ± 1 bar 150 ± 5 bar 2min (flow) 2 min (flow)

FIG. 12A is a photo of the surface of a wafer that has gone through apost ion implantation process but is not cleaned using a cleaningprocess according to an embodiment of the present invention. Photoresistresidues (opaque white dots) remain and protrude from the wafer having avariety of patterns including numbers.

FIGS. 12B and 12C are photos of the surface of the wafer of FIG. 12Athat has been cleaned using a cleaning process according to anembodiment of the present invention. Photoresist residues can be safelyremoved.

The cleaning additive including a fluoride group surfactant used in theabove-described embodiments may be used as the cleaning additive in theabove-described cleaning process. The fluoride group surfactant may usefluoride group carboxylic acid having a carbon number 2 to 20, perfluoroether system polymer having an average molecular weight of 300 to 5000or a mixture thereof.

In addition, like in the above-described embodiments, the cleaningadditive may include fluorosurfactant 0.01 to 90 wt %, aliphatic amine0.01 to 15 wt %, polar organic solvent 0.01 to 15 wt %, alcohol-basedsolvent 0.1 to 20 wt %, ether-based solvent 0.1 to 30 wt %,anticorrosive agent 0 to 5 wt %, and water 0 to 15 wt %. Here, 0 wt %means that a corresponding element is not included in the cleaningadditive, which is also applied to a later description.

In this case, fluorosurfactant may be fluoride group carboxylic acidhaving a carbon number of 2 to 20, perfluoro ether system polymer havingan average molecular weight of 300 to 5000 or a mixture thereof. Thealiphatic amine is monoethanolamine, 2-(2-aminoethoxy) ethanol,diethanolamine, amino bis propylamine, 2-methylaminoethanol,triethylaminoethanol or a mixture thereof. The polar organic solvent isN,N′-dimethylacetamide, dimethylsulfuroxide, 1-methyl-2-pyrrolidinone,N,N′-dimethylformamide, ammonium fluoride or a mixture thereof. Thealcohol-based solvent is methanol, ethanol, isopropanol or a mixturethereof. The ether-based solvent is ethyleneglycol methylether,ethyleneglycol ethylether, ethyleneglycol butylether, diethyleneglycolmethylether, diethylenglycol ethylether, triethyleneglycol methylether,triethyleneglycol ethylether or a mixture thereof. The anticorrosiveagent is catechol, gallic acid or a mixture thereof.

Like in the above-described embodiments, the cleaning additive mayinclude fluorosurfactant 0 to 90 wt %, semiconductor cleaning stripper0.1 to 15 wt %, alcohol-based solvent 0.1 to 20 wt %, and water 0 to 15wt %. In this case, the fluorosurfactant is fluoride group carboxylicacid having a carbon number of 2 to 20, perfluoro ether system polymerhaving an average molecular weight of 300 to 5000 or a mixture thereof.The alcohol-based solvent is methanol, ethanol, isopropanol or a mixturethereof.

Only the alcohol-based solvent may be used as the cleaning additive, andlike in the above-described embodiments, only the supercritical CO₂ maybe used in the process of rinsing the wafer, and the alcohol-basedsolvent may be methanol, ethanol, isopropanol or a mixture thereof.

In the supercritical homogeneous transparent phase mixture in which thesupercritical CO₂ and the cleaning additive used in the aboveembodiments are mixed, the cleaning additive was less than 30 percent byvolume. In addition, in the supercritical homogeneous transparent phasemixture in which the supercritical CO₂ and the cleaning additive used inthe above embodiments are mixed, the rinsing additive was less than 30percent by volume. In this case, the rinsing additive included methanol,ethanol, isopropanol or a mixture thereof.

As described above, in the cleaning apparatus and the high pressurecleaner thereof according to the present invention, the cleaning processcan be simplified, a time required for the cleaning process can bereduced and an excellent cleaning effect can be obtained.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A cleaning apparatus comprising: a liquid carbon dioxide (CO₂) supplysource and a gaseous CO₂ supply source; a high pressure pump changingCO₂ supplied from the liquid CO₂ supply source to CO₂ having highpressure; a cleaning additive supply source and a rinsing additivesupply source; a homogeneous transparent phase mixer forming asupercritical homogeneous transparent phase mixture by mixing a cleaningadditive supplied from the cleaning additive supply source andsupercritical CO₂ supplied from the liquid CO₂ supply source, or forminga supercritical rinsing mixture by mixing a rinsing additive suppliedfrom the rinsing additive supply source and supercritical CO₂ suppliedfrom the liquid CO₂ supply source; a high pressure cleaner cleaningusing the supercritical homogeneous transparent phase mixture suppliedfrom the homogeneous transparent phase mixer and performing rinsingusing the supercritical rinsing mixture supplied from the homogeneoustransparent phase mixer; a separator separating gaseous CO₂ from amixture discharged from the high pressure cleaner; and a CO₂ condensercondensing the separated CO₂.
 2. The cleaning apparatus of claim 1,further comprising at least one of a cleaning column and an adsorptioncolumn for purifying CO₂ separated by the separator.
 3. The cleaningapparatus of claim 1, wherein CO₂ condensed in the CO₂ condenser isprovided to the liquid CO₂ supply source and is re-used.
 4. The cleaningapparatus of claim 1, further comprising a heater heating CO₂ suppliedfrom the liquid CO₂ supply source, the cleaning additive supplied fromthe cleaning additive supply source, and the rinsing additive suppliedfrom the rinsing additive supply source.
 5. The cleaning apparatus ofclaim 1, wherein the homogeneous transparent phase mixer forms thesupercritical homogeneous transparent phase mixture by mixing thecleaning additive supplied having atmospheric pressure or a low pressureless than 10 bar with the supercritical CO₂ having high pressure of 120to 300 bar, using a large pressure difference therebetween.
 6. Thecleaning apparatus of claim 1, further comprising a pressure regulatingvalve connected to the high pressure cleaner and regulating pressureinside the high pressure cleaner.
 7. The cleaning apparatus of claim 1,further comprising: a circulation line connecting an outlet of the highpressure cleaner to a middle point between the high pressure cleaner andthe homogeneous transparent phase mixer; and a circulation pumpconnected to the circulation line.
 8. The cleaning apparatus of claim 1,wherein an internal or external circulation unit is provided to thehomogeneous transparent phase mixer.
 9. A high pressure cleanercomprising: a wafer loading device on which a wafer to be cleaned isloaded and which includes a protrusion; an upper element including aninlet through which a mixture is injected in a downward direction, awafer loading device fixing unit in which the protrusion of the waferloading device is inserted and which enables the wafer loading device tobe fixed therein, and a pneumatic cylinder insertion unit in which apneumatic cylinder sliding from a side is inserted; an ascending anddescending pneumatic cylinder moving the upper element in upward anddownward directions; a lower element including a pneumatic cylinderinsertion unit in which a pneumatic cylinder sliding from a side isinserted and an outlet through which a mixture is discharged and forminga space between the lower element and the upper element in which thewafer loading device can be disposed; and an adherent type pneumaticcylinder sliding into the pneumatic cylinder insertion unit of the upperelement and the pneumatic cylinder insertion unit of the lower elementand combining the upper element and the lower element when the upperelement descends and is engaged with the lower element.
 10. The highpressure cleaner of claim 9, further comprising a sealant disposedbetween an edge of a surface of the upper element in a direction of thelower element and an edge of a surface of the lower element in adirection of the upper element and sealing a space between the upperelement and the lower element from the outside.
 11. The high pressurecleaner of claim 10, further comprising a first bended portion disposedat an edge of a surface of the upper element in a direction of the lowerelement, and a second bended portion disposed at an edge of a surface ofthe lower element in a direction of the upper element, and a firstsealant and a second sealant disposed in the first bended portion andthe second bended portion, respectively.
 12. The high pressure cleanerof claim 9, wherein a groove is formed in a circumferential direction ofthe wafer loading device on a surface of the wafer loading device in adirection of the upper element, and a plurality of spray outlets areprovided along the groove.
 13. The high pressure cleaner of claim 12,wherein the inlet of the upper element is provided so that a materialinjected through the inlet of the upper element is injected in adirection of the groove of the wafer loading device.
 14. The highpressure cleaner of claim 9, wherein the upper element further comprisesan upper element guide pin and the lower element further comprises aguide pin insertion portion in which the upper element guide pin isinserted.
 15. The high pressure cleaner of claim 9, wherein the inletand the outlet are provided in opposite directions.
 16. The highpressure cleaner of claim 9, further comprising a heating source and acooling source controlling temperature of the high pressure cleaner.